A fuel vapor leakage sensing apparatus, which senses leakage of fuel vapor generated in a fuel tank, is known. For instance, JP2005-069878A (corresponding to US2005/0044937A1) recites a fuel vapor leakage sensing apparatus that uses a change valve to open or close connection between a passage, which is communicated with a fuel tank, and a passage, which is communicated with the atmosphere, or a passage, which is communicated with a pump. When a pressure in an inside of the fuel tank does not decrease to a first predetermined threshold value upon depressurization of the inside of the fuel tank with the pump, it is determined that the amount of leakage of the fuel vapor is equal to or larger than a limit value.
In the fuel vapor leakage sensing apparatus of JP2005-069878A (corresponding to US2005/0044937A1), a first valve element, which is formed separately from a valve shaft of the change valve, opens or closes an end portion of a communication passage synchronously with movement of the valve shaft of the change valve. In this case, the first valve element is tiltable relative to the valve shaft within a predetermined angular range to absorb variations in the perpendicularity and/or the coaxiality of each corresponding component. Thereby, at the valve closing time, when the first valve element is seated against a first valve seat upon tilting of the first valve element relative to the valve shaft, seal leakage may possibly be generated between the first valve element and the first valve seat. Since it is necessary to sense the leakage of the fuel vapor based on the pressure, which is measured at the valve closing time of the first valve element, the leakage of the fuel vapor cannot be accurately sensed in the case where the seal leakage is generated between the first valve element and the first valve seat.
Here, the seal leakage between the first valve element and the first valve seat can be sensed by determining whether the pressure, which is measured at the valve closing time of the first valve element, is within a predetermined pressure range. However, in the case where the seal leakage is generated due to the presence of the small amount of foreign object(s), it is not possible to sense the seal leakage between the first valve element and the first valve seat through the determination of whether the pressure, which is measured at the valve closing time of the first valve element, is within the predetermined pressure range. Therefore, when the seal leakage is generated due to the presence of the small amount of foreign object(s), an adverse influence may be imposed on the sensing accuracy of the fuel vapor leakage.